An IMS is a subsystem supporting IP multimedia service, which is proposed by the Third Generation Partnership Project (3GPP) in the fifth version thereof; the IMS is mainly featured by adopting the Session Initiation Protocol (SIP) and being independent of access. Under the development trend of network convergence, the 3GPP, the European Telecommunications Standards Institute (ETSI) and the International Telecommunication Union Telecommunications Standardization Sector (ITU-T) are researching a network convergence solution based on IMS, so as to achieve a is convergence of fixed network and mobile network; the IMS is thereby regarded as the ideal target architecture of the next generation network.
The concept of the Soft Switch (SS) had been gradually developed based on IP telephony since the late 1990s, and the soft switch technology had been gradually perfected in the process of transiting from narrowband to broadband and evolving from circuit switching to packet switching of the communications network. The soft switch has large-scale applications in the Internet; and it has been clear in the industry that IMS serves as a full-service target network of future fixed-mobile convergence (FMC); the evolving from the soft switch to IMS is an inevitable trend, of which the question to be considered firstly is how to enable the traditional fixed network access devices to access an IMS domain.
A traditional access device is generally registered by adopting a collectively registering way, namely, using a registration message to represent a collective access of all fixed network users under the access device, specifically with reference to a signalling from an Access Gateway (AG) to an Access Gateway Control Function (AGCF) side in FIG. 1. In IMS domain, a registration of the AGCF to a Call Session Control Function (CSCF) server is usually initiated with a Public User Identity (PUI) to which each independent user corresponds; the call session control function comprises a Service Call Session Control Function (S-CSCF), an Interrogating Call Session Control Function (I-CSCF) and the like; the S-CSCF is in a core dominate status in IMS, and is configured to registration, session control and process, and triggering service to an application server; an I-CSCF is an entry point from an access domain to a home domain, and is mainly in charge of interrogating information of home users, and allocating S-CSCF to users and the like. In FIG. 1, the two kinds of call session control functions are not differentiated, but the SIP signalling carries PUI that each independent user corresponds to needed to be transmitted between an AGCF and a CSCF is just schematically illustrated. A large amount of register messages may be generated at the same time, which makes a great impact on network traffic as well as a long registration time delay. Besides, the number of users under an access gateway usually reaches five or six thousand; if cases such as tolerant replace happen, a maximum number of users may reach two million in theory; and if multiple access gateways simultaneously initiate registration at that time, the resulting negative effects may be more serious.
In order to solve the problem that a large amount of register messages generated when registering from the AGCF to the CSCF causes negative effects to the network, it seems that an implicit register method in related standards may be taken as a reference; in Internet, a real user corresponds to a Private User Identity (PVI); at the same time, in network, the real user has multiple identities, namely corresponds to multiple PUIs; so a user actually has a PVI and multiple PUIs associated therewith; the user implicit register method means to initiate registration with the PVI to which each independent user corresponds; thus, if a user is registered successfully, it is implied that all the user's different PUIs are registered successfully, thus there is no needed to initiate register messages of PUI one after another, so as to reduce the network traffic and registration time delay. However, an implicit register itself cannot effectively solve the problems above, for the following reasons: 1) the implicit register clearly represents different PUIs of the same PVI only, and the essence thereof is to enable different identities of the same user to be registered, however, users of a traditional H248 root fixed network represent bulk users; so they are two inconsistent concepts and the implicit register cannot be directly applied; 2) a size of an implicit set is limited, and generally, only 8-12 user identities are allowed to be registered at the same time, but there are hundreds of access gateways frequently, so the capacity of the implicit register method cannot meet an access request of a large number of fixed network users; 3) because the implicit set represents the different identities of the same user, it has the limit of ‘living together and dying together’; specifically, living together means that if the PUI of a user registers to access a service, all the other PUIs of the user access the service; and if the PUI of a user reports to quit a service, inevitably, all the other PUIs of the user are triggered to quit the service.